Surveying a bridge used to involve drilling into the road to check the concrete and steel structures underneath. Although radar has simplified the work since the 1980s, sending out teams of people to check bridges is still expensive and can require extended road closures. Human inspections aren’t immune to error either, as the I-35W case shows. The upshot is that many bridges are overdue a health check – thousands in the US alone, for instance.

To address these issues, Spencer Gibb at the University of Nevada and his colleagues have built the first fully autonomous robot bridge inspector – one that shuttles back and forth along the side of the road without getting in the way of passing traffic.

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The four-wheeled, waterproof, battery-powered device uses ground-penetrating radar and electrical resistivity sensors to locate any corroded steel parts or deteriorating concrete inside the bridge. Surface cracks can be detected using the on-board camera.

Maps of weakness

A machine-learning algorithm converts the readings in real time into a colour-coded map of the bridge, highlighting any areas of weakness. The results are sent to human inspectors, who can keep tabs on the robot as it does its rounds.

The team tested the robot on four road bridges in Nevada, New Hampshire, Maine and Montana, where it proved speedier and more accurate than human inspectors. “The robot takes the same amount of time to physically scan the bridge as a human inspector but it processes the data in minutes instead of hours,” says Gibb. The team is now working on ways to cut down the inspection time of the robot as well.

Another benefit is that one robot is cheaper than a team of people, says Gibb. When human inspectors check a bridge, other workers are needed to close it off to traffic and analyse the data.

Tommy Chan at the Queensland University of Technology in Australia says the cost-effectiveness will ultimately depend on how the robot compares with other upcoming technologies like drones and sensors built into bridges themselves.

Chan believes that robots should be a complementary technology for bridge inspections. “Human experience is precious so, at least for now, I don’t see robots replacing humans altogether,” he says. “But robots do cut out human error so we should definitely consider them as a way to help.”